Vacuum die casting



Nov. 27, 1962 R. w. PARKER 3,065,510.

VACUUM DIE CASTING Filed May 27, 1960 2 Sheets-Sheet 1 I INVENTOR.

Nov. 27, 1962 Filed May 27, 1960 R. w. PARKER 3,065,510

VACUUM DIE CASTING 2 Sheets-Sheet 2 United States vania Filed May 27, 1960, Ser. No. 32,170 1 Claim. (Cl. 22-73) This invention is a cold chamber vacuum die casting machine which evacuates air from the cold chamber and mold cavity without entraining molten metal which would clog the vacuum lines.

In the drawing, FIG. 1 is a diagrammatic view of a die casting machine, FIG. 2 is a vertical transverse section through the pour opening and cold chamber, FIG. 3 is a section on line 33 of FIG. 1, FIG. 4 is an enlarged fragmentary view showing the behavior of the metal during evacuation, and FIG. 5 is a similar view at right angles to FIG. 4.

In the drawing, the conventional elements of the die casting machine are readily identified, 1 being the stationary platen, 2 the movable platen, 3 and 4 the stationary and movable parts of the mold, 5 the cold chamber into which metal 6 is poured through a pouring hole or opening '7, and 8 the knockout plate carried on rod 9 and having knockout pins 10' slidable through the movable mold 4 to eject the cast parts as the mold is opened. In the sequence of operations, after the mold is closed molten metal is poured into the cold chamber 5 through the opening 7, partially filling the chamber, and this metal is forced by a water cooled pressure piston or shot plunger 11 through sprue opening 12 into the mold cavity 13. After filling of the mold cavity, the mold is opened and during the opening movement the knockout pins 10' eject the finished parts and sprue from the movable mold part 4. No attempt has been made to describe the die opening and closing mechanism. The controls and the associated structure are common to die casting machines. The parts so far described are in common use in the die casting industry and may differ substantially in appearance from those illustrated.

The mold parts 3 and 4 carry sealing rings 1-4 and 15 providing a sealed chamber surrounding the parting line 17 of the mold. The movable mold part 4 is sealed to an annular ring 18 surrounding the back surface of the mold and providing a chamber 19 between the back surface of the mold and the movable platen 2. The knockout plates 8 and pins 10 operate within the chamber 19. The chambers 16 and 19 are maintained under vacuum by a vacuum line 20 connected to a suction pump 21. The parts so far described are disclosed in greater detail in application Serial No. 745,943, filed July 1, 1958, now abandoned.

While there is some evacuation of the mold cavity through the vacuum maintained in the chambers 16 and 19, the primary evacuation is in the cold chamber 5 under the control of a slide valve 22 having a way 23 connected to a line 24 leading to the Vacuum pump 21. The slide 22 is of circular cross section and is slidably guided in a bore 25 in the cold chamber 5. In the position shown in FIG. 2 an opening 27 in the slide registers with the pouring hole 7 for the cold chamber so that molten metal can be poured into the chamber by any suitable means. In this position, the way 23 is sealed against the inner surface of the bore 25. When the desired amount of molten metal has been poured into the cold chamber 5 (enough to partially fill the cold chamber as shown in FIGS. 1 and 2), the slide 22 is moved to the left as viewed in FIG. 2, bringing the way 23 into register with a way 29 (FIG. 3) leading to a restricted space 30 between the end 31 of the plunger 11 and the adjacent surface of the cold chamber. The space 30 is conveniently formed by a taper 32 on the end of the plunger which provides an annular crack between the extreme outer end 31 of the plunger and the inner surface of the cold chamber. The width of the crack is such that the molten metal will not flow by gravity into the space 30. This is a well-known property of metal. For the temperatures encountered in die casting, molten metal will not flow into a crack having a width of the order of fifty thousandths of an inch. This is true even if the space 30 is evacuated so that the molten metal is also subjected to atmospheric pressure. Furthermore, since the plunger 11 is cooled, the metal coming into initial contact with the outer end of the plunger is chilled as indicated at 34 and this still further restricts the possibility of flow of molten metal into the space 30. There may be some slight bowing of the metal into the space 30 as indicated at 35, but for all practical purposes the metal is eifectively kept out.

While the space 30 is a restricted space so far as the molten metal is concerned, it is a very large opening so far as air is concerned and in no way interferes with the evacuation of the cold chamber and mold through the suction way 29. If difiiculty is encountered in speed of evacuation, the upper part of the cold chamber below the way 29 may be crowned as indicated by dotted lines 36 in FIGS. 4 and 5 and this will still further enlarge the space through which air may flow into the suction way 29. The crowning indicated by dotted lines 36 do not in any way permit molten metal to enter the space 30. The level of molten metal indicated by numeral 37 is well below the top of the cold chamber and is also well below the enlargement produced by the crowning 36. Under the suction there is some fiow of air in the direction of arrows 38 and 39 but the greater part of the air flows in the direction of the arrows 40 which is in a direction in which there is little tendency for the air to pick up and entrain droplets of molten metal. Even if particles of molten metal were picked up by the air, they would not flow into the narrow crack between the cold chamber and the outer end 31 of the plunger.

This construction eliminates a very troublesome problem in vacuum die casting. Where the vacuum is applied directly above the surface of molten metal such as would be the case if it were applied directly to the pour opening 7, the air picks up and entrains fine droplets of molten metal which follow the air, even as far as the pump. While it is possible to separate from the air a few droplets of metal by the use of traps and similar separators, if more than a few droplets of metal are entrained, the entrainment of molten metal is progressive and very quickly a solid mass of molten metal is drawn into the suction lines, forcing a machine shut-down. With the present construction, this is not possible. In the first place, the air is sucked out of the chamber over the chilled outer end of the plunger where the molten metal has already begun to set up. Furthermore, the highest velocity air which would have the greatest tendency to pick up molten metal, flows through a crack so restricted that molten metal will not flow through the crack under atmospheric pressure. It is accordingly possible to obtain a high degree of evacuation of the space above the metal in the cold chamber and of the mold cavity without running the risk of metal entrainment. When the evacuation is completed, the shot plunger 11 is advanced and the metal in the cold chamber is forced under high pressure into the mold cavity. Of course, under pressure the metal is forced into the space 30 surrounding the end 31 of the plunger. However, when the mold is opened at the end of the cycle, the metal which filled the space 30 is part of the sprue and is forcibly separated from the outer end 31 of the plunger so that at the beginning of the next cycle the space 39 is open.

The vacuum can be added to existing die casting machines Without modifying the control. As the slide valve 22 is moved to the pouring position shown in FIG. 2, a valve 23 in line 24 is opened. When the pouring is completed, the slide 22 is moved to the vacuum position connecting the Way 23 with the way 29 and evacuating the cold chamber and mold cavity. The evacuation takes only a few seconds. A simple timer or other control set in operation by movement of the slide valve 22 to the vacuum position can shut the valve 23 when the desired vacuum is reached and initiate the machine control to complete the casting cycle. The closing of the valve 28 prevents connection of the vacuum line 24 to the atmosphere when the mold is opened at the end of the casting cycle.

What is claimed as new is:

A die casting machine of the cold chamber type in which the molten metal is first delivered to the cold chamber and then mechanically transferred to a mold cavity under pressure comprising, a horizontal cold chamber cylinder closed at one end by a shot plunger having a tapered end and connected at the other end to a mold, said cylinder having a pour opening in its upper part adjacent said one end of the cylinder and in front of the shot plunger in its retracted position through which a charge of molten metal may be poured into the cold chamber cylinder when the shot plunger is in its retracted position, said charge partially filling the cold chamber cylinder and leaving a space above the metal communicating with the mold cavity, said cylinder having a way in the upper part opposite the tapered end of the shot plungerin the retracted position, the tapered end of the shot plunger providing a crack between it and the part of the cylinder having said way, said crack having a maximum width of the order of fifty thousandths of an inch so that air will flow freely from the cold chamber into the crack but molten metal will not flow into the crack under atmospheric pressure and the crack is metal free in back of the molten metal after delivery of metal to the cold chamber, suction means, valve means for closing said pour opening and for connecting said suction means to said way to evacuate the cold chamber and the mold cavity through said crack without entraining molten metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,059 Pack Nov. 14, 1933 1,954,775 During et al Apr. 10, 1934 2,774,122 Hodler Dec. 18, 1956 2,955,335 Morgenstern Oct. 11, 1960 3,019,495 Cornell Feb. 6, 196 2 

